Kozel: CNS Infections II Flashcards
Gram positive, ovoid or lancet shaped, in pairs; old cultures are gram variable; aerobic
Encapsulated
Strep pneumo
Older cultures of S. pneumo undergo (blank); the autolytic enzymes are activated by surfactants such as (blank) and detergents
autolysis; bile
What is the major antigen of S. pneumo? What is another antigen of this microorganism?
capsular polysaccharide; C polysaccharide (techoic acid) in the cell wall
What type of antigen is the capsular polysaccharide of Strep pneumo? Is it essential for the virulence of S. pneumo?
T-independent antigen; yes
incubation of encapsulated bacteria with antibody makes capsule refractile; seen with Strep pneumo
Quellung reaction
What infections do S. pneumo cause?
meningitis (most common cause among young and elderly)
otitis media (most common cause in children >3yo)
pneumonia (80-90% of bacterial meningitis)
sinusitis
What kind of pathology does S. pneumo initiate?
abrupt onset, toxicity, DIC
inflammatory response to the bacterium and its products
**the bacteria initiates the inflammatory response, but avoids being killed by it
3 virulence factors of S. pneumoniae?
- polysaccharide capsule - essential, prevents phagocytosis
- pneumolysin - contributes to inflammation
- peptidoglycan and lipoteichoic acid - cell wall components, activate alternative pathway, elicit production of IL1 and TNFalpha, largely responsible for inflammatory response
Components of cell wall of S. pneumoniae
Activate alternative pathway
Elicit production of IL-1 and TNFa
Largely responsible for inflammatory response
peptidoglycan and lipoteichoic acid
Virulence factor of S. pneumo;
Porin similar to Streptolysin O
Contributes to inflammation; multiple effects
pneumolysin
40-70% of normal individuals carry pneumococci in the nasopharynx, so (blank) is very high
natural resistance
What are some natural defensive barriers to pneumococcal infection?
cough and epiglottal reflex
mucus and cilia
phagocytosis by alveolar macs
splenic clearance from blood
List 5 conditions that alter resistance to strep pneumo
- depressed action of cilia - viral infection or influenza
- depressed epiglottal reflex - alcohol, morphine, anesthesia
- hyposplenia or asplenia - decreased clearance from blood
- sickle cell disease
- malnutrition
Sudden onset with shaking chill, fever and sharp pleural pain
Bloody, rusty sputum
Generally localized in lower lobes
pneumococcal pneumonia
What specimens can you use to diagnose S. pneumo infection?
sputum
body fluids: blood, CSF, pus
How can you differentiate S. pneumo from viridans streptococci?
- alpha hemolytic (they both are)
- optichin sensitive (viridans is resistant)
- bile soluble
What antigen would you be looking for in a S. pneumo serologic test?
pneumococcal C polysaccharide
How does S. pneumo enter the body?
upper resp tract
Unlike N. meningitidis and Hib, most healthy adults do not have (blank) to S. pneumo
anticapsular antibody
Composition: Purified capsular polysaccharide
Polyvalent (23 serotypes) – covers 94% of bacteremic cases
Action – induction of opsonic antibody
Case-control studies indicate 60-80% efficacy
Titers persist at least 5 yrs; little or no booster effect
T-independent antigen – not effective for
Pneumovax and Pnu-Imune
Who is the pneumovax recommended for?
all adults 65+
anyone 6-18yo w specific risk factors
**not for children under 2yo!!
Composition: polysaccharide-protein conjugate
Polyvalent (13 serotypes) – covers >80% of bacteremic disease and 65% of acute otitis media among children <6 yrs
T-dependent antigen
Prevnar 13
Who is the Prevnar vaccine recommended for?
all children 2-59 months
>65yo
children at risk ages 6-18
So, there are two vaccines used to prevent pneumococcal infection. One is a multivalent (23) purified capsular polysaccharide. What is it? The other is a 13-valent polysaccharide-protein conjugate. What is it?
Pneumovax and Pnu-Imune; Prevnar 13
Drug of choice for treating pneumococcal infection?
penicillin or cefriaxone if susceptible
if resistant, try vancomycin, macrolides, doxycycline, or a quinolone
What is the mechanism of resistance that pneumococcal bacteria have against penicillins?
acquire a penicillin binding protein with reduced affinity for the antibiotic
What should you give to treat pneumococcal meningitis?
ceftriaxone or penicillin + vancomycin
- *ceftriaxone is more effective and has better CNS penetration
- *vancomycin if resistance to B-lactam antibiotics
Does penicillin cross the normal BBB? What allows it to cross in cases of meningitis?
no; inflammation increases permeability
When penicillin goes to work, it kills bacteria and release peptidoglycan and teichoic acids from the cell walls. What do these products do? What can be given to avoid this reaction?
PG and TA cause intense inflammatory reaction, contributing to increased intracranial pressure and irreversible brain damage; can reduce inflammatory response by use of corticosteroids
Synonym: S. agalactiae
Normal flora of genital (10-30% of normal women) and gastrointestinal tracts
Leading cause of neonatal sepsis and meningitis; extremely high mortality rate
Systemic disease in adults compromised by diabetes, cancer or HIV infection
Group B streptococci
What is the key virulence factor of Group B streptococci?
antiphagocytic capsular polysaccharide
T/F: Antibody to capsular polysaccharide of Group B strep is protective and also protective for newborn children
True
What can group B strep cause during the first week of life? At ages 1 week to 3 months? In adults?
bacteremia, pneumonia, meningitis;
bacteremia and meningitis;
bacteremia, pneumonia, bone/joint infection and skin/soft tissue infection (usu in older pts with underlying conditions)
What are some risk factors for early onset group B strep infection?
exposure to bacterium from the genitals or GI (found in 10-40% of women), prolonged membrane rupture, or intrapartum fever
absence of anticapsular antibody - the mother doesn’t have the antibody or delivers prior to 37 weeks gestation
How can you identify group B strep in the lab?
gram stain: gram positive cocci
beta hemolytic
agglutination test for Lancefield group B antigen
How do we prevent group B strep infection in neonates?
screen all pregnant women at 35-37 weeks gestation for vaginal or rectal colonization
give intrapartum antibiotic prophylaxis at time of labor or rupture of membranes, also give to prego women who test positive for GBS colonization
How do you treat Group B strep infection?
penicillin G; emperic treatment - ampicillin + an aminoglycoside
When do you give intrapartum Group B strep antibiotic prophylaxis?
previous infant w invasive GBS disease
GBS bacteriuria during current pregnancy
positive GBS screening during current pregnancy
GBS status unknown but deliver at 18hours, intrapartum temp elevated
Encapsulated yeast
Opportunistic infection
Four serotypes of capsular polysaccharide
A, B, C and D
Termed CrAg (cryptococcal antigen)
Assay for CrAg is foundation for diagnosis
Two species
C. neoformans (serotypes A and D)
C. gattii (serotype B and C)
Globally, most serious and life-threatening of the pathogenic fungi
Cryptococcus neoformans
How do you get cryptococcois infection?
environmental sources - pigeon droppings, trees
What population is Cryptococcosis most commonly seen in?
HIV/AIDS patients, mostly in Sub-Saharan Africa
What are two major clinical syndromes caused by Crypto neoformans?
- pulmonary cryptococcosis - relatively common with C. gattii
- cryptococcal meningitis - most common clinical form, fatal if untreated
What are other manifestations of Crytococcus neoformans?
skin lesions
ocular infection
prostatic involvement
opportunistic infections in AIDS patients and organ transplant recipients
What test is used to diagnose crypto?
India ink stain of CSF to look for encapsulated yeast
What antigen would you look for in cases of cryptococcosis that would be useful in diagnosis?
CrAg - capsular antigen
use latex agglutination, enzyme immunoassay, or lateral flow immunoassay
How to treat crypto infection?
antifungal agents: amphotericin B, flucytosine, fluconazole
3 phases of crytococcosis treatment?
- induction - amph B + flucytosine + fluconazole
- consolidation - fluconazole
- maintenance - fluconazole
Occurs at initiation of HAART
Overwhelming inflammatory response to previously acquired OI
Immune reconstitution inflammatory syndrome (IRIS)
How to prevent cryptococcal disease?
screen and treat!
screen all AIDS patients for serum CrAg before starting ART
treat all CrAg + individuals before ART
**this will save 100,000 lives per year!
